A display apparatus includes a backlight module, a driving module, and a power circuit. The driving module receives an external pulse width modulating (PWM) signal and transmits the signal to the power circuit. The power circuit outputs a working current for driving the backlight module based on the PWM signal. The driving module calculates a working cycle of the PWM signal and adjusts the PWM signal to be in a high frequency range with the constant calculated working cycle of the PWM signal to avoid audio noise being generated in the driving process and for the backlight module to remain at a predetermined brightness. Based on the calculating process, the backlight module may be lit after a certain time.